#6 San Diego, California

The San Diego metro area had a 42% increase in total number of unhealthy ozone pollution days since 2015. While clean car standards are effective, rising temperatures are increasing the frequency of ozone days.

Getty Photo Source: Sandy Huffaker / Stringer

#5 Sacramento, California

Some Sacramento regions have experienced an average increase of 9 bad ozone days, with per annum days totaling nearly one month.

Getty Photo Source: David Paul Morris / Stringer

#4 Fresno, California

In one of its west side neighborhoods, where freeways, agriculture, and industry commingle, air pollution has proven particularly troublesome.

#3 Visalia, California

The city of Visalia, with thousands of trucks traveling daily on the adjacent Highway 99, suffers from particulate and smog air pollution.

Getty Photo Source: David McNew / Stringer

#2 Bakersfield, California

With a strong petroleum industry presence, Bakersfield's air pollution is exacerbated by agriculture, rail freight, and automobile emissions.

Getty Photo Source: FREDERIC J. BROWN / Staff

#1 Los Angeles, California

La La Land tops the list for American cities with the most harmful ozone pollution. A recent study indicated that 53% of urban air pollution may come from consumer products such as hair spray and cleaning agents.

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